Known is a construction machine including a boom, for example, a travelling-type crane, the construction machine including a slewing body supporting the boom so as to allow the boom to be raised and lowered. Slewing the slewing body and the boom supported on the slewing body enables omnidirectional craning work in an entire periphery around an own machine to be performed, and raising and lowering the boom allows a crane operation at a high position or a position far from the slewing body to be done. These enable a load operation to be done in a three dimensional space.
Raising the boom causes a force in the boom to compress the boom itself. Furthermore, application of lateral force such as wind power or slewing inertial force to the boom generates large lateral bending moment to bend the boom laterally, thereby causing the boom to be laterally deflected. Besides, the boom may have not only the lateral deflection but also torsion. Such lateral deflection or torsion involves change of the boom in its shape, namely, deformation thereof.
Japanese Unexamined Patent Publication No. 2012-51713 discloses a technique to suppress such deformation of a boom. The technique includes attaching a lateral mast crossing a longitudinal direction of a main boom to extend in a lateral direction, and extending a tension rope between both ends of the lateral mast and a sheave provided at a front end of the main boom.
The technique, however, requires attachment of various members including the lateral mast, the sheave, and the tension rope to the main boom, and adjustment thereof, thus involving an increase in scale of facilities and an increase in costs.